Telephone system



Oct. 14,1941.` H. HovLAND i TELEPHONE SYSTEM Filed Feb. 2l, 1940 II II JIIOIII /NvENToR H. H0 VL AND Patented ct. 14, 1941 TELEPHONE SYSTEM Henry Hovland, Williston Park, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 21, 1940, serial No. 319,993

e claims. l(ci. 179-18) This invention relates to telephone systems and particularly to systems comprising impulse controlled selector switches for use in establishing connections between calling and called lines.

Objects of the invention are the simplica- .L

tion of the switching means employed in establishing telephone connections and the prevention of, and improvement in, arrangements for limiting the service and preventing the completion of calls to which a subscriber is not entitled.

One feature of this invention is a two-motion selector switch arranged to transmit a busy tone to the calling subscriber upon selection of a restricted level and to automatically advance the brushes to the eleventh rotary step position, the test circuit through the test brush being opened during advance over the terminals of a restricted level so as to prevent the connection of a busy-indicating and guarding potential to the test terminals in this level.

`A second feature of this invention is a twomotion digit absorbing selector having a control relay for effecting the secondary motion'after one or more digits have been absorbed and so arranged as to prevent false operation of the control relay incase the selector is seized on a second call during its return to normal at the end of a first call.

The invention will be more clearly understood by considering a switch in `which the invention is embodied, one such switch being shown in the drawing which forms a part of this specification. The invention is not limited in its application to the switch shown in the drawing but is generally applicable to all two-motion selector switches.

The drawing shows schematically a subscribers station A and line LI, a line-finder switch LF, a selector S, trunk circuits 52 and 53, a connector C, and a called subscribers station B. The line-finder, selector and connector switches are of the well-known twomotion step-by-step type. Reference may be had to pages 53 to 65, inclusive, of the second edition Automatic Telephony, by Smith and Campbell, for a description of the structure of such switches and their operation when used as selectors and connectors. The line-finder LF is similar to that disclosed in the patent to R. L. Stokely 1,799,654, issued April 7, 1931. The linefinder and connector switches` are represented in the drawing by a set of brushesand a single set of terminals, the stepping magnets and control relays associated therewith being omitted.

Although the selector S is shown in the drawing as being permanently associated with the line-iinder LF, it is understood that there may be `one or more intermediate selectors between the line-iindcr LF and selector S and that the selector S may be used as an incoming selector in which case it is connected to an interoflice trunk.

The selector S, which is shown in detail, comprises a set of brushes 3|, 32 and 33, a vertical stepping magnet 2 I, a rotary stepping magnet 22, a release magnet 29, vertical off-normal springs 23, 11th rotary step springs 24, level springs 25 and 26, and control relays l5, I6, Il, I8, I9 and 2i); The brushes may be advanced by operation of the vertical stepping magnet to select any one of ten levels of terminals, each level comprising ten terminals. After selection of 4a level,

' the brushes may be advanced by operation of the rotary stepping magnet into engagement with an unguarded set of terminals in that level or in 'case all of the ten sets of terminals test busy to an llthrotary position. Only three sets of terminals are shown in the drawing, the set 4l representing a level in which the brushes have access to succeeding switches inthe same oice, the set 42 representing a level in which the brushes have access to interoflice trunks, and the set 43 representing the 10th or O level in which the brushes have access to trunks to an operator. The selector S is arranged to absorb one or more digits and for this purpose is provided with a set of springs 25 which are actuated on the level or levels corresponding to digits of the particular numerical value or values which are to be absorbed. The selector S is also provided with a set of springs 26 which are actuated on one or more restricted levels, that is, -levels corresponding to the iirst digits of the numbers of subscribers to which calls from subscribers served by the selector S may be completed only by calling an operator. If a restricted surface level is selected, the brushes are advanced to the 11th rotary step position and an all-trunks-busy tone is transmitted to the calling subscriber. Since thev terminals of the bank of selector S may be multipled to selectors serving subscribers entitled to complete calls to a group of trunks connected to the restricted level or levels of selector S, the actuation of springs 2E is effective to prevent the connection of a busyindicating potential to the test brush during the advanceto the 11th rotary step position.

Assuming a call to have been originated at station A and the line LI to have been connected through the brushes of line-finder switch LF (and through intermediate selectors, if any), to the selector S, a circuit is closed from battery through the lower winding of relay I5, inner lower back contact of relay I8, brush I2 of the line-finder switch LF, one conductor of line LI, through the subscribers instrument at station A, back over the other conductor of line LI, through brush I I of switch LF, upper back contact of relay I8, upper winding of relay I5, upper normally closed contact of the 11th rotary step spring 24, a lower back contact of relay 20, and through the left winding of the dial tone source 21 to ground. Relay I5 is operated by the current in this circuit and cio-ses a circuit for operating relay I6. Relay IC- connects ground to conductor `35 to hold the line-finder LF in usual manner. is transmitted to the calling subscriber if the selector S is being used as a rst selector, as shown in the drawing. When the subscriber at station A dials the iirst digit of the number of the subscribers line with which connection is desired, relay I5 is alternately released and reoperated as many times as there are units in the digit dialed. The release of relay I5 in response to the rst impulse closes a circuit from ground at a back contact of relay I5, through a back contact of relay I5, a front contact of the relay I6, winding of relay II and through the Winding of magnet 2I to battery. The vertical stepping magnet 2l and relay II are operated by the current in this circuit. The operation of magnet 2I steps the brushes 3|, 32 and 33 up to the first level of the bank. The vertical olinormal springs 23 are actuated when the shaft and brushes, move out of normal position, thereby closing a circuit for operating relay I9, from battery through the winding of this relay, the lower back contact of springs 24, the upper contact of springs 2,2, front contactv of relay I1 to ground at a back contact of release magnet 29. Relay I 9 closes a locking circuit which includes the lower back` contact of springs 24, the upper contact of springs 22, the back contact of the rotary stepping magnet 232', inner front contact of relay I9, conductor 3,4 and the inner right front contact of relay I6. When relay I5 releases at the endof the rst impulse, the stepping magnet 2l releases; but relay Ij'I is a slow-to-release relay and remains operated until all of the impulses in the train have been received. Relay I6 is also slow to release and remains, operated during the response of relay I5 to dial impulses. Each succeeding release and reoperation of relay I5 effects a corresponding operation and release of stepping magnet 2I, thereby raising the brushes, step by step, to the level corresponding to the digit dialed.

Assume rst that the called subscriber is in another oilice and that the selected level is not a restricted level and is represented by the set of terminals 2 connected to the outgoing trunk circuit 52. In this case. the level springs 2 5 and 2 5 are not actuated on the selected level and the release of relay I'I, upon reoperation of relay I5 after the last dial impulse of the train, closes a circuit for operatirlgthe rotary stepping magnet 2 2. This circuit is from battery through the winding of magnet 22, normally closed contact of springs 25, inner upper back contact of relay 2i), outer iront contact of relay I9, inner back contact,A of relay- I'I, to ground at a back contact of.4 the release magnet 29. The operation of magnet 22 advances the brushes into engagementA with the rst set of terminals in the Selected level androgens the Circuit threlieh Dial tone the winding of relay I9. Relay I9 releases caisii ing the release of magnet 22. If the trunk circuit connected to this set of terminals is busy, the test brush 33 encounters ground potential which is extended through the lowermost back contact of relay I8, normally closed contact of springs 25, uppermost back contact of relay 20, outer back contact of release magnet 29, back contact of magnet 22, upper contact of springs 2-3, lower back contact of springs 24 and through the winding of relay I9 to battery. Relay I9 is thereby reoperated to again close the circuit for operating rotary stepping magnet 22, and the reoperation of magnet 22 steps the switches into Engagement with the next set of terminals in the level. The magnet 22 and relay I9 are in this manner effective to continue the stepping of the brushes until the terminals of an idle trunk are encountered. There being no ground potential on the terminal engaged by test brush 33 if the associated trunk is idle, the release of magnet 2 2 closesk a circuit for operating relay I8. This circuit is from battery through the winding of relay I?, the lower back contact o f springs 24, upper contact of springs 273, back contact of magnet 22, back contact of release magnet 29, winding of relay I8, conductor 30 to ground at` a front contact of relay I5, Being marginal, relay I9 is not operated by the current in this circuit. Relay I8 extends the connection from line LI through its front contacts and through brushes SI and 32 to the trunk or other circuit connected to the seized terminals. The operation of relay I8 also causes the release of relays I5 and I6. Since relay I5 is slow in releasing, ground is connected through its outer left front contact, conductor 3U, outer lower front contact of relay i8 and brush 33 to mark the test terminals of the seized trunk circuit busy until this circuit connects ground thereto responsive to its seizure. After relay I8 releases, the line-finder LF and relay I8 of selector S are held through brush 33 to ground in the outgoing trunk or repeater circuit 52. Reference may b e had to Fig. 67 and pages '70 to '72, inclusive, o the aforementioned second edition of Automatic Telephony for a complete disclosure of such an outgoing trunk circuit.

The impulses created by the dialing of the remaining digits of the called subscribers number are repeated by the outgoing trunk circuit 52 to effectI the operation of an incoming selector, intermediate selectors, if any, and a connector in the called o ce in usual manner to extend the connection to the called subscribers line, If the line isV idle, the subscribers station is sig,- naled; and, when the call is answered, the desired conversational connection is complete.v

When the calling subscriber releases the connection by restoring the receiver to normal, the outgoing trunk circuit disconnects the holding ground from the terminal engaged by brush 33, thereby causing the release of relay I8 and the release of the line-under LF. The; release of relay I8 closes a circuit from ground at its mid'- dle lower back contact, through back contacts of relays I5 and I6, the lower front` Contact of springs 23, and through the winding of release magnet 2 9 to battery. The release magnet 29 operates and it locks under control of springs 23. The operation of magnet. 29. causes the return of the shaft and brushes of selector S to normal. When theshaftk reachesk normal', pQsition. the springsl 23, are restored to4 normal position, opening the circuit through the winding of magnet.29.`

. .If all of the trunks connected to the terminals of a selected level are busy, the step-by-step advance of the brushes in this level continues in the manner above described until the brushes reach the 11th rotaryposition in which position the 11th rotarystep springs 24 are actuated to prevent the further reoperation of'relayv I9 and rotary lstepping magnet 22. The actuation of springs 24 connects the right WindingV of busy tone source 28 to the upper Winding of relay I so as to transmit an all-trunksbusy' tone to` the' calling subscriber. When the calling subscriber releases the connection by replacing the receiver', relays I5 and I 6 release; and, since relay I8 is not operated, the release magnet 29 is operated and the selector S is restored to normal as above described.

` Assume next that the subscriberat station A is calling anotherA subscriber in' the same office in which case the iirstdi'git dialed is to be absorbed.l In this case, thesprings are actuated when the brushes are raised tothe selected level. The release of relay I1 at the end of the impulse train closes a circuit for operating the vrelease magnet 29. 'This circuit is traced from batt-ery' through the Winding of magnet 29, lower contact of springs 23,"front contact of springs 25, a back contact of relay 29, iront contact of relay I9, back contact of relay I1, to ground at a back contact of magnet 29. Before this operating circuit is opened at the back Contact of magnet 29, a holding circuit is closed through the inner front contact of magnet 29 and the lower contact of springs 23. The operation of magnet 29 effects the return of the shaft and brushes to `normal position.y The springs 25 return to normal when the brushes leave the selected level;

and the springs 23 are restored when theshaft andbrushesreach normal, thereby causing the release of magnet 29 andrelay I9. While magnet 29 is actuated to restore the shaft and brushes to normal, a circuit is closed for operating relay 29. This circuit includes the outer front contact of magnet 29, the inner front contact of relay I9, `conductor 34, and front Contact 'of relay I6. VRelay 29 locks through its inner upper front contact,the outer back contact of "relay II, and conductor 34, to ground at the front contact of relay I6. `Relay 29 disconnects the dial `tone source and connects ground direct- `ly to thev upper Winding of relay I5. When the calling subscriber dials the second digit of the called subscribers number, the alternate release and reoperation of relay I5 causes the operation of vertical magnet 2| and relay Il, as above described, the brushes 3l, 32 and 33 being stepped up to the level corresponding to this digit. The operation of relay I'I and actuation of springs 23 cause the reoperation of relay I9 and relay I9 locks as` above described. Relay I'I opens the locking circuit of relay 29 and relay 29 releases. If the level selected in response to the second digit dialed is one on which the springs 25 are again operated, the second digit is also absorbed by returning the brushes to normal in the same manner as that in which the iirst` digit Was absorbed, relay 29 being reoperated and again locked as above described. If the level selected in respense to the second digit, or a succeeding digit,

doesnot effect return of the brushes to normal, the release of relay Il after the last impulse of the train has been received closes the circuit for operating the rotary stepping magnet 22 and the brushes are' stepped into engagement With an idle set of terminals as above described. The operation of relay I8, when an idle circuit is encountered, effects the release of relays I5 and I6 and extends the connection from the calling line through brushes 3I and 32 to an intermediate selector circuit (not shown) or ldirectly to a connector circuit C. Relay I9 is held operated, after relays I5 and I6 release, by the connection of ground y(in the seized circuit) to the terminal engaged by brush 33. The release of relay I5 causes the release of relay 29. The dialing of the remaining digits of the called subscribers number effects the operation of intermediate selectors (if any) and the connector C to complete the desired connection. When the calling subscriber releases the connection, the holding ground is disconnected from the terminal engaged by brush 33 and relay I8 releases, -causing the return of selector S to normal.

If the calling subscriber is a restricted service subscriber and dials the iirst digit of a number outside ofthe local area, springs 29 are actuated when the brushes are raised to the corresponding level. The actuation of spring 26 connects ground through the uppermost back contact of relay 29 and outer back contact of magnet 29 vto the back contact of the rotary stepping magnet 22, thereby causing the repeated reoperation of relay I9 and magnet 22 to advance the brushes to the 11th rotary position in the manner hereinbeiore described. opening of the back contact of springs 29 prevents the connection of ground potential to the 1;. terminals engaged by test brush 33 duringad- Vance of the brushes to the 11th rotary position so that these terminals will not be falsely marked busy. Busy tone is transmitted to the calling station as hereinbefore described.

Each time Vthat av connection is completed through the selector S, the operation of relay I8 closes a circuit for operating the messageregister 35. As soon as relay I6 releases, this circuit is opened and the register releases. The register 35, therefore, gives an indication of the number of calls completed through the selector S.

It is to be particularly noted that the circuit for operating relay 29 includes a front contact of relay I9. This is to prevent the `false operation of relay 29 in ca'se the selector S is seized, or otherwise connected to a second calling line, While the release magnet 29 is energized responsive to release of the connection from a `iirst calling line. While such a seizure and false operation may in some cases be prevented by connecting a guarding potential to the release conductor 39 While the release magnet 29 is operated, such an arrangement would not be effective to prevent reseizure and a possible false operation of relay 29 if the selector S is used as an incoming selector. YSince relay I9 is not energizing until a rst series of impulses has been received, a false operation of' relay 29 is prevented in the case of both local and incoming selectors Without connecting a guarding potential to the release conductor 39 during the release operation.

What is claimed is:

1. In a selector switch, `a bank of terminals,

The"

matically advancing said wipers to the `first set ci terminals in the selected group, means iiiclud'i'ngthe test wiper for' testing each lset of terminals Aengaged by the wipersand for conf tinuing theladvance of the wipers from one set ofterminals'to the next until the wipers en` gage the terminalsof an idle trunk, saidlastf mentioned means being effective to advance the wipers to the all-trunks-busy position if all of the trunks in the selected group are busy, and means comprising contacts actuated when Ya particular one of said groups is selected for causing the advance of said wipers to the all-trunks-busy position irrespective of whether there is or is not an idle trunk in the selected group and for disconnecting the test wiper during said advance.

2. I n a telephone system comprising subscribers lines and a selector switch for use in completing calls between calling and called lines, groups of trunks connected to the bank of said switch, an over-How position for each of said groups of trunks, means for directively oper ating said switch to select a desired group or trunks, means for automatically operating said switch to select an idle trunk in a selected group or to advance the wipers to the over-flow position in case all of the trunks in the group are busy, said last-mentioned means comprising a test circuit including the test wiper of the switch, and a set of contact springs actuated upon selection of a certain one of said groups for causing the advance of the wipers to the over-flow position and for opening the connection te the test wiper during said advance.

3. In a telephone system, a selector switch comprising a set of brushes and a bank of terminals, said terminals being divided into groups, trunks connected to said terminals, means for seizing said switch, means for directively advancing the brushes to select any one of said groups, means for automatically advancing the brushes in a selected group, means effective when the brushes engage a set of terminals connected to an idle one of said trunks for stopping the advance of said brushes to seize said set of terminals, means comprising a release magnet for restoring said brushes to normal position, means comprising Contact springs actuated upon selection of a particular group for preventing the automatic advance of the brushes in said group and for operating said release magnet to restore the brushes to normal, a relay, a circuit for operating said relay, said circuit closed by the operation of said release magnet, and relay means for preventing the closure of said circuit incase the operation of said release magnet is subsequent to the seizure of a set of terminals in a selected group.

4. In a two-motion digit absorbing selector comprising a set of brushes, a terminal bank divided into levels, means for directively operating the selector in a primary movement to select a level, means comprising a test relay for automatically operating said selector to select a set of terminals in a selected level, a release magnet for restoring the brushes to normal, a set of contact springs adapted to be actuated upon selection of a particular level of the terminal bank, vand a relay controlling the initiation of the secondary operation, a circuit for operating said release magnet to absorb a digit, said circiut comprising a front contact of said set of contact springs, acircuit for operating said control relay comprising a front contact of said release magnet, a second circuit for operating said release magnet, and means comprising contacts of said test relay for preventing the operation oi" said control vrelay upon operation of said release magnet by the closure of said second operating circuit. 5. In a selector switch, a'shaft carrying a set o f brushes, a bank of terminals divided into levels, a primary magnet for advancing said brushesto select a desired one of said levels, a secondary magnet for advancing the brushes in any selected level, an impulse receiving relay for controlling said primary magnet, a stepping relay for controlling the voperation of said secondary magnet, a circuit for operating said' stepping ref lay comprising a set of vertical ofnormal con-,- tact springs actuated upon advance of said shaft from normal position, a circuit comprising a back contact of said secondary magnet for holding said stepping relay until the secondary magnet is operated to advance the brushes into engage@ ment with the rst set of terminals in a selected level, a circuit comprising a back contact of said secondary magnet and one of said brushes for testing the busy or idle condition of each set offterminals andior reoperating said stepping relay if the engaged set of terminals tests busy, a switching relay for effecting seizure of the first idle set of terminals encountered, a control relay, a second set of shaft operated contact; springs, said second set of contact springs adapted to be actuated upon selection of a particular level, a first circuit for operating said secondary magnet comprising a normally closed contact of said second set of contact springs, a back contact of said control relay and a front contact of said stepping relay, a second circuit for operating said secondary magnet comprising a front contact of said control relay and said front contact of said stepping relay, a release magnet for restoring said brushes to normal position, a first circuit for operating said release magnet comprising a front contact of said second set of contact springs, a back Contact of said controly relay and a front Contact of said stepping relay, a Acircuit for operating said control relay comprising a front Contact o f ysaid release magnet and a front .Contact of said stepping relay, yand a second circuit for operating said release magnet comprising back contactsof said impulse receiving and switching relays. l 6. In a two-motion group selector switch comprising a set of brushes and a bank of terminals divided into levels', means for directively ladvancing said brushes tohselect any one of Said levels and means including a test relay for automatically advancing the brushes to selectv an idle set of terminalsl in the selected level,l a set of contact springs adapted to be actuated when the brushes are kadvanced to a particular level, and means including said test relay effective upon actuation of said springs for advancing'the `brushes over all of the" vterminals in said particular level irrespective of their busy or idle condition to a position beyond the last set 'of terminals in the level, said springs also being effective when .actuated lto open the connection between said test relay and 'the test brush to prevent the connection Aof a busy indicating potential to the test terminal of thesets of terminals passed over 'during the advance Vto said position.

HENRY HOVLAND. 

